COST AND PERFORMANCE REPORT

Transcription

1 October 22, 1999 COST AND PERFORMANCE REPORT Soil Vapor Extraction Enhanced by Six-Phase Soil Heating at Poleline Road Disposal Area, OU-B, Ft. Richardson, Alaska October 1999 Hazardous, Toxic, Radioactive Waste

2 SITE INFORMATION IDENTIFYING INFORMATION (1) Site Name: Poleline Road Disposal Area (PRDA) Location: Fort Richardson, Alaska Operable Unit: OU-B ROD Date: August 8, 1997 Technology: Soil Vapor Extraction (SVE) Enhanced by Six-Phase Soil Heating (SPSH) Type of Action: Treatability Study Figure 1 shows the location of the Fort Richardson in Alaska. Figure 2 shows the layout of the PRDA. TECHNOLOGY APPLICATION (1,2,8,9) Period of Operation: Treatability Study July through December 1997 Quantity of Material Treated During Application: 3,910 cubic yards (CY) or 7,150 tons of solvent-contaminated soil Three cylindrical arrays were used for the treatability study. Two of the arrays were 27 feet in diameter and one array was 40 feet in diameter. All three arrays were designed to treat soil from 8 to 38.5 feet below ground surface (bgs). For arrays 1 and 2, the soil treatment zone extended past the array perimeter by at least 5 feet (40% of the array radius) based on pre- and post-treatment soil analyses. Removal beyond the array perimeter was not demonstrated in array 3. BACKGROUND Site Background (1,3,4): Fort Richardson was established in 1940 as a military staging and supply center during World War II. It originally occupied 162,000 acres approximately 10 miles northeast of Anchorage, Alaska. In 1950, Fort Richardson was divided between the Army and Air Force. Fort Richardson now occupies approximately 56,000 acres and is located adjacent to Elmendorf Air Force Base. Fort Richardson was added to the U.S. EPA s National Priority List (NPL) in June In December 1994, the Army, Alaska Department of Environmental Conservation (ADEC) and EPA signed a Federal Facilities Agreement (FFA) that outlined the procedures and schedules required for a thorough investigation of suspected historical hazardous substance sources at Fort Richardson. The FFA divided Fort Richardson into four Operable Units. The PRDA, designated as OU-B, was identified in 1990 through interviews conducted by the U.S. Army with two ex-soldiers who were stationed at Fort Richardson in the 1950s and who recalled the disposal of chemicals and other materials in the area. The disposal location was corroborated by a U.S. Army Corp of Engineers (USACE) map dated 1954 showing a Chemical Disposal Area at the PRDA and by a 1957 aerial photograph showing trenches in the area. The disposal area was active from approximately 1950 to Hazardous, Toxic, Radioactive Waste Page 1

3 Figure 1. Location of Fort Richardson in Alaska Hazardous, Toxic, Radioactive Waste Page 2

4 Figure 2. Layout of the Poleline Road Disposal Area Hazardous, Toxic, Radioactive Waste Page 3

5 Previous investigations identified four disposal areas at OU-B. Chemical warfare agents and training materials, smoke bombs, Japanese cluster bombs, and other materials were neutralized and disposed in trenches at PRDA. Geophysical surveys have delineated the waste disposal areas to be approximately 1.5 acres in size. SIC Code: 9711 (National Security) Waste Management Practices that Contributed to Contamination (1): Chemical warfare agents, smoke bombs, Japanese cluster bombs (detonated prior to burial), and other materials were neutralized and disposed at PRDA. The procedure was to first place a layer of bleach/lime in the bottom of the trench. A pallet with the materials to be disposed was placed on top of the bleach/lime layer. Diesel fuel was poured on the materials and ignited with thermal grenades. After burning was complete, a mixture of either bleach or lime, combined with a chlorinated solvent carrier, was poured over the materials. When disposal was completed, the trenches were backfilled to match the surrounding grade. Site Investigations and Remedial Actions (1,3,4,9): Several site investigations and a removal action have been conducted at the PRDA since its discovery in 1990: Between 1990 and 1992, site investigations were conducted which included a geophysical survey, soil sampling from 10 borings, a soil gas survey, installation of 11 groundwater monitoring wells, groundwater sampling, a water level study, and aquifer (slug) tests. The investigation identified the location of the trenches, buried debris, and solvent contamination in the soil and groundwater. In 1993 and 1994, a removal action in areas A-3 and A-4 was conducted. This effort was interrupted due to the discovery of chemical agent identification sets and other chemical warfare training activities. A geophysical survey was conducted in early 1994 to better identify the location of buried objects in these areas. Areas A-3 and A-4 showed the greatest evidence of buried waste and trenching, including possible stacked canisters or cylinders. Contaminated debris and soil were excavated to a maximum depth of 14 feet, where groundwater was encountered, and the excavation was backfilled with clean soil. During this removal action, sampling confirmed that chlorinated solvents were in the soil below the water table. Excavated soil was treated on-site by heat enhanced SVE in two static piles. A geophysical survey was performed in June 1995 to determine whether any buried material remained in the recently excavated areas and to more accurately define anomalous zones in areas not excavated in 1993 and Based on the geophysical survey, areas A-1 and A-2 are expected to contain less significant quantities of buried waste, and therefore smaller volumes of contaminated soil, than areas A- 3 and A-4. At the time of this report, areas A-1 and A-2 had not been excavated or sampled. Information provided by an ex-soldier previously stationed at Ft. Richardson indicated that undetonated bomblets from cluster bombs might be buried in these areas. In August and September 1995, a remedial investigation (RI) was conducted that included collection of soil, groundwater, surface water, and sediment samples from the site and background areas. Soil samples beneath the previous excavations in Area A-3 exceeded the cleanup criterion for 1,1,2,2-tetrachloroethane used during the excavation. Hazardous, Toxic, Radioactive Waste Page 4

6 Since the completion of the RI in 1995, soil and groundwater sampling and testing has been ongoing at the site to generate data for various treatability studies and to further delineate the nature and extent of contamination. A treatability study was conducted in the fall of 1996 as part of a feasibility study for OU-B. The treatability study included tests for SVE, air sparging, pump testing to determine aquifer characteristics, and groundwater sampling for intrinsic remediation parameters. The study concluded that SVE was capable of removing vapors from the subsurface, but at a rate that would require more than 10 years of treatment. Based on these results, it was recommended that SVE treatment enhanced with in-situ soil heating could be used at the site as a means for completing treatment more rapidly. A human and ecological risk assessment was completed in September The risk assessment concluded that the site poses no imminent threat to human health or the environment based on a lack of complete exposure pathways under current and probable future use scenarios. However, if groundwater were to be used as a source of drinking water or if buildings with basements were constructed at the site, groundwater and soil gas could pose unacceptable risks. SITE LOGISTICS/CONTACTS (1,2) Role Site Lead Oversight Regulatory Contact(s) Contact Information Kevin Gardner U.S. Army, Department of Public Works Fort Richardson, Alaska (907) Bernard T. Gagnon, P.E. (no longer with USACE) USACE, Alaska District P.O. Box 898 Anchorage, Alaska Lewis Howard Alaska Department of Environmental Conservation (ADEC) 555 Cordova Anchorage, Alaska (907) LHoward@envircon.state.ak.us Matt Wilkening US EPA Region th Street Seattle, Washington (206) wilkening.matt@epamail.epa.gov Hazardous, Toxic, Radioactive Waste Page 5

7 Contractor Technology System Vendor Scott Kendall Woodward-Clyde Federal Services (now URS Corporation) 3501 Denali Street, Suite 101 Anchorage, Alaska (907) David Fleming Current Environmental Services, LLC P.O. Box Bellevue, Washington (425) MATRIX AND CONTAMINANT DESCRIPTION MATRIX IDENTIFICATION Soil (in situ) SITE GEOLOGY/STRATIGRAPHY (1,3,4) A 1979 soil survey described most of the soil at PRDA as a Homestead silt loam. The Homestead silt loam is described as a well-drained soil formed over gravelly till. The underlying till varies in compactness and is extremely firm in some areas. Soil matching the Homestead series is found over most of the site, except for the wetlands area where soil is included in the Salamatof series. The Salamatof is a nearly level, poorly drained soil consisting of fibrous peat materials that occur in broad basins and depressions on terraces and moraines. The subsurface soil sampled during the RI were glacial tills, generally described as silty sands with some gravel. Silt, sand, and gravel were observed in nearly every sample at various percentages. Clay-sized particles were observed in very few samples. The soil was of high density, with blow counts during drilling often greater than 50 blows per 6 inches. Four separate water-bearing intervals have been identified at PRDA. These water-bearing intervals are a perched interval, a shallow interval, an intermediate interval, and a deep aquifer. All four intervals appear to be interconnected to some degree. Zones of high-density tills separate the saturated intervals. Groundwater is encountered at a depth of 4 to 14 feet bgs. The deep aquifer and glacial tills overlie bedrock composed of a hard black fissile claystone with fine sandy siltstone interbeds. Bedrock is encountered from approximately 80 to 170 feet bgs and has an unknown thickness. Hazardous, Toxic, Radioactive Waste Page 6

8 CONTAMINANT CHARACTERIZATION (1) Primary Contaminant Group: Organic Compounds Volatiles (Halogenated) Key Specific Contaminants: 1,1,2,2-Tetrachloroethane (TCA) Tetrachloroethene (PCE) Trichloroethene (TCE) CONTAMINANT PROPERTIES (4,5,6) Table 1 lists selected properties for the key specific contaminants at OU-B. Table 1. Contaminant Properties Property Units TCA PCE TCE Chemical Formula - Cl 2 CH CHCl 2 Cl 2 C=CCl 2 Cl 2 C=CHCl Molecular Weight g/mole Specific Gravity - 20 C 20 C 20 C Boiling Point C Vapor Pressure mm Hg 20 C 20 C 20 C Water Solubility mg/l 25 C 25 C 25 C Octanol-Water Partition Coefficient log K ow Soil-Sediment Sorption Coefficient log K oc Flammability - Not Flammable Not Flammable LEL 8% UEL 10.5% NATURE AND EXTENT OF THE CONTAMINANTS (1,3,4) Two solvents, TCA and TCE, were found in higher concentrations and over a larger area than any other chemicals detected. PCE was also detected above action levels. Results from the 1995 RI indicated the presence of TCA in the soil at a maximum concentration of 2,030 mg/kg. Contaminants were detected in each of the four saturated intervals. These results indicate that there is interconnectivity between the saturated intervals, which has allowed the contaminants to migrate vertically. The highest concentrations of TCA (1,900 mg/l) and TCE (220 mg/l) were detected in the perched interval. The removal action eliminated the major source of contaminants migrating to the groundwater. However, two sources may remain: solvent-contaminated soil beneath and potentially west of the previous excavations and dense non-aqueous phase liquids (DNAPLs). DNAPLs were observed in a monitoring well during the FS. Comparison of dissolved phase concentrations of solvents to their water solubilities indicated that DNAPLs are present in the subsurface. Soil excavated from areas A-3 and A-4 was sampled and compared to the following maximum allowable concentrations (as designated for the removal action). These concentrations were drawn from U.S. EPA Region 10 s risk-based concentrations using a 10-5 exposure risk; soil exceeding the criteria was stockpiled for treatment. TCE mg/kg, PCE mg/kg, and TCA - 30 mg/kg. Hazardous, Toxic, Radioactive Waste Page 7

9 Soil samples were collected from borings drilled around the perimeter of areas A-1 and A-2 and through the fill at areas A-3 and A-4. Concentrations of contaminants in soil outside of the disposal areas are generally well below removal action levels. None of the samples collected from the fill soil exceeded the removal action criteria used during the excavation. However, two soil samples collected beneath the previous excavation in area A-3 had levels of TCA which exceeded the removal action criteria. The highest concentrations of contaminants detected in soil and groundwater samples were found in Areas A-3 and A-4 in a hot spot area of approximately 150 feet by 300 feet. Soil sampling data indicated that there was a layer of soil with high contaminant concentrations starting at around 16 feet bgs and extending to around 27 feet bgs in this area. Figure 2 shows the approximate location of the hot spot. Lower concentrations of contaminants were detected in the soil and groundwater near areas A-1 and A- 2 (soil and groundwater within areas A-1 and A-2 were not sampled due to the potential presence of unexploded ordnance). Trends in the contaminant concentrations suggest that contaminants detected near the saturated intervals in areas A-1 and A-2 migrated from areas A-3 and A-4 in the direction of groundwater flow. Contaminants do not appear to have been released in areas A-1 and A-2, except for potential surface spills that may have been the source for contaminants detected in shallow soil near area A-2. Historical information indicates that it is unlikely that chemical warfare materials were disposed in areas A-1 or A-2, and therefore, chlorinated solvents were not needed for neutralization. Groundwater modeling performed using MODFLOW and MT3D estimated that the solvents would not reach the nearest downgradient receptor (Eagle River) for over 100 years. MATRIX CHARACTERISTICS AFFECTING TREATMENT COST OR PERFORMANCE (3,4,6,8) Table 2 lists selected characteristics of untreated soil from OU-B. Table 2. Matrix Characteristics Parameter Value Measurement Procedure Soil Classification SP gravelly sand Unified Soil Classification System GP sandy gravel GM silty sandy gravel Clay Content and/or Particle Size Low clay content; silt, sand and Visual Distribution gravel observed Moisture Content % Method 7-2.2, Methods of Soil Analysis Air Permeability 1.6 x 10-7 cm 2 Calculated using field measurements and steady state equation Porosity 21 27% Estimated from Grain Size Depth bgs or Thickness of Zone 8 to 35 feet bgs Not Applicable of Interest Total Organic Carbon % ASA Presence of Nonaqueous Phase DNAPL found in a 2 monitoring Visual Liquids (NAPLs) well Electrical Conductivity Acceptable Not Available Hazardous, Toxic, Radioactive Waste Page 8

10 PRIMARY TREATMENT TECHNOLOGY (1) TREATMENT SYSTEM DESCRIPTION Soil In Situ Soil Vapor Extraction In Situ Heating (Six-Phase Soil Heating) SUPPLEMENTARY TREATMENT TECHNOLOGIES (1) Post-treatment (Air) Condenser Post-treatment (Air) Catalytic Oxidation (only used during the beginning of the study) Post-treatment (Water) Air Stripping TREATMENT SYSTEM SCHEMATIC AND TECHNOLOGY DESCRIPTION AND OPERATION Figure 3 shows a process flow diagram for the SPSH SVE system used to treat in-situ soil at OU-B. Initial Activities (2,8) The contractor mobilized to the site in June Pre-treatment soil samples were collected from the areas covered by each array. Three arrays were constructed and operated at the OU-B site. The array 1 SPSH and SVE system was installed in June System shakedown at array 1 occurred from July 1 through July 10, The array 2 SPSH and SVE system was installed in August The array 2 shakedown period lasted approximately two weeks due to grounding problems that prevented effective soil heating. The array 3 SPSH and SVE system was installed in October Only two days were needed for shakedown at array 3. Technology Description and Operation (1,2) General Description of SVE Enhanced by Six-Phase Soil Heating SPSH is a patented, multi-phase electrical technique that utilizes common power line frequency (60 Hz) to resistively heat soil. SPSH can turn groundwater into steam that will strip volatile and semivolatile contaminants from the soil. The steam stripping facilitates movement of contaminants from low permeability zones into more permeable zones where the contaminants are removed by the SVE system. In situ heating also allows the contaminants to volatize more readily. Electrical power is delivered throughout the area being treated by steel electrodes inserted vertically into the soil. The electrodes are placed in a circular array consisting of six electrodes on the periphery and one electrode in the center. Each periphery electrode is connected to one of the six single-phase transformer wires. Six conventional single-phase transformers convert standard three-phase electricity into six-phase electricity at the desired voltage. Each electrode is operated at a different voltage phase, so the electricity conducts with all the other electrodes in proportion to the voltage differences. The electrode spacing and the connected electrical phases are both 60 degrees apart, resulting in a uniform ratio of voltage difference to physical distance between all electrodes in the array. The result is a relatively even heating pattern. The seventh neutral electrode is located at the center of the array. Each electrode also serves as an SVE vent. Hazardous, Toxic, Radioactive Waste Page 9

11 Figure 3. Process Diagram Hazardous, Toxic, Radioactive Waste Page 10

12 The electricity will follow the path of least resistance between two electrodes. Saturated fine-grained soil has high conductivities, so the electricity will initially flow readily through this type of soil. As the soil is heated, the conductivities will change. These changes occur when the groundwater is turned to steam and is removed by the SVE system. By removing the groundwater, the moisture content and consequently the conductivity of the soil is reduced. As the moisture content decreases, the electricity will find a more conductive path through the soil. More electrical energy is required to maintain the system due to reductions in the conductivity. This is offset by increased air permeability of the dry soil, which enhances vapor recovery. Site-Specific Description After the initial system shakedown period, the three arrays were operated at the OU-B site. Each array was operated for a six-week period. A 455-kW diesel generator powered arrays 1 and 2. Array 3 used a 1200 kw diesel generator. Initially, two 500-gallon aboveground storage tanks supplied diesel for the generators. Additional aboveground storage tanks were added during operation of array 3 so that refueling trips could be reduced. Each generator supplied 3-phase, 480-volt power to the six-phase transformer and to other equipment on site. The electrodes were installed in a circular array 27 feet in diameter for arrays 1 and 2 and 40 feet in diameter for array 3. All of the arrays were installed to heat soil from 8 to 38.5 feet bgs. The screened interval for each electrode extended from 10 to 20 feet bgs. This interval was selected to ensure that rising steam was captured by the SVE system and to intercept the most highly contaminated zone. Electrodes consisted of galvanized steel casings surrounded by granular graphite to enhance current flow. An 8-foot section of 6-inch diameter CPVC was placed over the upper portion of the casing to electrically isolate the upper 8 feet of soil from the electrode. This prevented active heating of the upper 8 feet of soil. Quarter-inch drip tubes were attached to each electrode to allow for the injection of water into the soil immediately surrounding the electrode. Soil close to the electrode has a tendency to dry before the majority of the soil has completely heated. The decrease in soil conductivity requires higher voltages to be applied. By adding a small amount of water adjacent to the electrode, the conductivity is increased and the voltage requirements are lowered. Based on a November 1996 feasibility study conducted at OU-B, the radius of influence of the SVE system was estimated at 25 feet. The SPSH treatability study was conducted at similar vacuum flow rates as demonstrated in the feasibility study. A 20-hp positive displacement blower was used to pull soil vapors from the extraction wells through a knockout tank to remove any solids from the hot vapors before entering a condenser. Copper coils in the knockout tank reheated any condensed vapors. The condenser cooled the vapors pulled from the extraction wells and separated the liquid and vapor phases. The gas phase passed through a second knockout tank prior to the blower to remove residual condensable vapors. This condensate and the liquid phase from the condenser were preheated and then pumped through an air stripper that used ambient air. After treatment, the air stripper effluent was used in the electrode drip tubes with the excess water discharged to area A-2. During initial operations at array 1, a catalytic oxidizer was used to treat off-gas from the blower. Since the concentration of solvents in the off-gas was less than expected, the oxidizer was removed from the site before treatment at array 1 was completed. System Operation and Monitoring Operation of the treatment system was automated, but was monitored and adjusted daily. The major system adjustments that could be made at each electrode included the electrode voltage, the water drip flow rate, and the SVE system vacuum. Voltages were adjusted to maintain a constant power input to the Hazardous, Toxic, Radioactive Waste Page 11

13 electrodes of approximately 400 kw. Higher voltages were required to maintain the desired power input as the soil dried and the soil conductivity decreased. The computer that monitored the six-phase transformer calculated the phase resistance at each electrode. The water flow rate was increased to electrodes that had higher resistances. While the test was running, several parameters were monitored to help estimate the performance of the system. Some parameters were monitored by electrical sensors and automatically recorded by the on-site computer. These parameters included: Condenser off-gas pressure, flow, and temperature; Soil temperature from thermocouples placed at locations within each array that would be the last to heat; Transformer voltages, amperages, and total power; and Soil resistivity. Other parameters were observed and manually recorded from various gauges. These parameters included: Generator amperage; Fuel levels; Vacuum at SVE knockout tanks; Off-gas photoionization detector levels; and Effluent water tank levels. Post-Operation (1,2,8) Treatment system shutdown and demobilization occurred in December Post-treatment soil samples were collected in January After operation of the treatment system, no additional restoration activities (e.g., final grading, landscaping) were necessary at the site. Personnel Requirements (8) Operation of the treatment system normally required one person on-site 8 hours per day, 5 days per week, and several hours each weekend day. An off-site project manager spent several hours each day managing the project (e.g., calling the client, locating parts, working with subcontractors, etc.). Health and Safety Requirements (4,8) For the RI, initial drilling operations were performed in Level B personal protective equipment (PPE), which included supplied breathing air and chemical resistant clothing, boots, and gloves. Approximately halfway through the field investigation, the health and safety requirements were reviewed and approval was granted by the USACE to downgrade to Level D PPE. The downgrade was requested because no chemical warfare materials had been detected in the area most likely to be contaminated. All work related to the treatment system was performed in Level D PPE. During drilling operations, fans were used to dissipate solvent vapors. OPERATING PARAMETERS AFFECTING TREATMENT COST OR PERFORMANCE (1,2,3,8) The following table lists values for parameters associated with operation of the SVE system at PRDA OU-B. The parameters were selected for this report based on USACE guidance. Hazardous, Toxic, Radioactive Waste Page 12

14 Table 3. Operating Parameters Parameter Design Actual Soil ph Not Applicable Soil Temperature 100 C C after 2 weeks Electrical Power Input 455 kw (Arrays 1 and 2) 1,200 kw (Array 3) 400 kw (Arrays 1 and 2) kw (Array 3) Air Flow Rate of the SVE System Not Available acfm (20ºC and psia) Operating Pressure/Vacuum of the Not Available inches water SVE System Condenser Flow Rate Not Available 600 gal/day Condenser Temperature Not Available 140 C Inlet Ambient Outlet TIMELINE (1,2) Date Activity 1990 The OU-B site was identified Preliminary investigations conducted at the site Removal action conducted at the site June 1994 Fort Richardson added to the NPL December 1994 FFA signed by the Army, ADEC and EPA August - September 1995 Remedial investigation conducted September 1996 Human and ecological risk assessment completed January 1997 Feasibility study completed August 8, 1997 ROD signed by U.S. EPA Region X Administrator June 1997 Site mobilization, system set-up, and collection of pre-treatment soil samples July 1 10, 1997 System shakedown July 11 August 22, 1997 Treatment conducted at Array 1 August 24 October 9, 1997 Treatment conducted at Array 2 November 6 December 18, Treatment conducted at Array December 1997 January 1998 Demobilization and collection of post-treatment soil samples PERFORMANCE OBJECTIVES (1,2) TREATMENT SYSTEM PERFORMANCE System performance was evaluated against three primary criteria: The ability of each six-phase heating array to heat soil in-situ; Demonstrated removal of contaminants, as measured in the condenser off-gas and condensate; and Demonstrated reduction of soil contamination, as measured by the pre- and post-treatment soil sampling results. The air stripper was operated so that the effluent concentrations were below Alaska s maximum contaminant levels (MCLs) for drinking water. Table 4 presents the MCLs for contaminants of concern at the site. Hazardous, Toxic, Radioactive Waste Page 13

15 Table 4. Alaska Maximum Contaminant Levels (3) Chemical Alaska MCL (m /L) Benzene 5 Carbon Tetrachloride 5 Chlorobenzene Not Established Chloroform 100 1,4-Dichlorobenzene Not Established 1,2-Dichloroethane Not Established 1,1-Dichloroethene 7 cis-1,2-dichloroethene 70 trans-1,2-dichloroethene 100 Hexachloroethane Not Established TCA Not Established PCE 5 Toluene 1,000 1,1,2-Trichloroethane 5 TCE 5 TREATMENT PERFORMANCE DATA (1,2) Figure 4 presents temperature profiles for each of the three arrays. Each thermocouple boring provided temperature readings at three depths within the arrays. Condenser off-gas and condensate were sampled to determine concentrations of contaminants extracted by the system. Off-gas and condensate were collected from the condenser approximately every other day during operation. The off-gas samples were collected in summa canisters and sent to an analytical laboratory for volatile organic chemical (VOC) analysis by EPA Method TO-14. Water samples were analyzed for VOCs by EPA Method 8260A. Table 5 presents the condenser off-gas sample results for arrays 1, 2, and 3. Condensate results from the three arrays are provided in Table 6. These results were used to calculate the mass of contaminants removed in the off-gas and condensate, respectively. While data was collected for a standard list of VOCs, only results for TCA, TCE and PCE are presented in these tables. Air stripper effluent results for TCA, TCE, and PCE are also provided in Table 6 for comparison to influent concentrations. Sampling of the effluent was terminated once the air stripper demonstrated the ability to comply with the Alaska MCLs. Soil samples were collected to determine pre- and post-treatment soil concentrations. Pre-treatment soil samples were collected during drilling for the thermocouple borings, and post-treatment soil samples were collected by drilling a boring adjacent to the thermocouple boring. Sampling at array 1 included two borings within the array and two outside the array. Sampling at arrays 2 and 3 each included one boring within the array and one outside the array. Sample locations are shown on Figure 2. Soil samples were analyzed for VOCs by EPA Method 8260A. Table 7 presents a comparison of soil samples taken pre- and post-treatment. Results for the principal contaminants of concern at OU-B (TCE, PCE and TCA) are shown in the table. Detection limits were used to calculate removal efficiencies for samples where contaminants were not detected. Hazardous, Toxic, Radioactive Waste Page 14

16 Figure 4. Temperature Profiles Within the Arrays Hazardous, Toxic, Radioactive Waste Page 15

17 Table 5. Contaminant Concentrations in Condenser Off-Gas (ppmv) Array Sample Date TCA TCE PCE 1 7/15/ /19/ /21/ /24/97 condenser /24/97 catox /29/ /31/ /2/ /4/ /6/ /8/ /12/ /16/ /18/ /26/ /29/ /5/ /10/ /20/ /23/ /25/ /27/ /29/ /1/ /4/ /18/ /20/ /22/ /24/ /26/ /28/ /30/ /2/ /4/ /6/ /8/ /10/ /12/ /14/ /16/ /18/ Hazardous, Toxic, Radioactive Waste Page 16

18 Array Sample Date Condensate/Air Stripper Influent Table 6. Contaminant Concentrations in the Condensate (mg/l) TCA TCE PCE Air Stripper Effluent Condensate/Air Stripper Influent Air Stripper Effluent Condensate/Air Stripper Influent Ft. Richardson PRDA OU-B Air Stripper Effluent 1 7/15/97 53, , ND (1) 7/19/97 130, , ND (1) 7/21/97 41, , ND (1) 7/24/97 15, , ND (1) 7/29/97 14, , ND (1) 7/31/97 20,000 NS 2,700 NS 33 NS 8/2/97 14,000 NS 2,100 NS 38 NS 8/4/97 11,000 NS 1,600 NS 25 NS 8/6/97 13,000 NS 1,700 NS 33 NS 8/8/97 19,000 NS 2,200 NS 15 NS 8/10/97 25,000 NS 2,700 NS 17 NS 8/12/97 18,000 NS 2,300 NS 15 NS 8/16/97 6,500 NS 1,400 NS 8 NS 8/18/97 14,000 NS 2,000 NS 13 NS 2 8/26/97 8,900 NS 2,400 NS 33 NS 8/29/97 12,000 NS 2,900 NS 49 NS 9/10/97 8,500 NS 1,400 NS 20 NS 9/20/97 8,800 NS 1,800 NS 34 NS 9/23/97 5,700 NS 1,900 NS 43 NS 9/25/97 3,200 NS 1,200 NS 24 NS 9/27/97 5,200 NS 3,300 NS 57 NS 9/29/97 8,100 NS 1,500 NS 30 NS 10/1/97 2,600 NS 890 NS 14 NS 10/4/97 4,000 NS 1,300 NS 17 NS 3 11/18/97 20,000 NS 2,200 NS 33 NS 11/20/97 12,000 NS 1,300 NS 20 NS 11/22/97 8,800 NS 1,800 NS 28 NS 11/24/97 19,000 NS 4,600 NS 64 NS 11/26/97 7,400 NS 1,500 NS 21 NS 11/28/97 8,300 NS 1,800 NS 27 NS 11/30/97 4,900 NS 1,200 NS 17 NS 12/2/97 11,000 NS 1,800 NS 33 NS 12/4/97 8,500 NS 1,600 NS 25 NS 12/6/97 7,100 NS 1,300 NS 23 NS 12/8/97 4,700 NS 920 NS 15 NS 12/10/97 2,800 NS 590 NS 10 NS 12/12/97 3,100 NS 1,100 NS 13 NS 12/14/97 3,900 NS 1,200 NS 15 NS 12/16/97 3,600 NS 1,100 NS 14 NS 12/18/97 3,600 NS 1,100 NS 14 NS NS Not Sampled. Sampling of the air stripper was stopped once the unit demonstrated the ability to comply with the Alaska MCLs. Hazardous, Toxic, Radioactive Waste Page 17

19 Array Sample ID Table 7. Pre- and Post-Treatment Soil Concentrations (mg/kg) TCA Concentrations PCE Concentrations TCE Concentrations Sample Depth (ft) Pre-Treat Post-Treat % Removal Pre-Treat Post-Treat % Removal Pre-Treat Post-Treat % Removal 1 T-A ND (0.07) ND (0.05) ND (0.05) Inside ND (0.05) ND (0.05) Array D ND (0.06) ND (0.06) D D ND (0.06) ND (0.06) ND (0.05) 88 ND (0.05) ND (0.05) ND (0.05) 88 ND (0.06) ND (0.05) T-A ND (0.07) ND (0.06) ND (0.06) ND (0.055) Inside D ND (0.05) ND (0.05) Array D ND (0.05) D D ND (0.06) D ND (0.06) D T-A ft ND (0.05) ND (0.05) Outside Array ND (0.05) ND (0.06) ND (0.05) 99 ND (0.05) ND (0.05) T-A ND (0.06) ND (0.06) ft ND (0.06) Outside Array Hazardous, Toxic, Radioactive Waste Page 18

20 Table 7 (Continued) Ft. Richardson PRDA OU-B Array Sample ID TCA Concentrations PCE Concentrations TCE Concentrations Sample Depth (ft) Pre-Treat Post-Treat % Removal Pre-Treat Post-Treat % Removal Pre-Treat Post-Treat % Removal 2 T-A ND (0.06) D ND (0.05) ND(0.05) Inside ND (0.05) ND (0.05) Array ND (0.05) ND (0.05) D ND (0.05) ND (0.05) D ND (0.06) ND (0.06) ND (0.06) NS - ND (0.06) NS NS NS NS NS - 2 T-A ND (0.05) 55 ND (0.05) ND (0.05) ft ND (0.05) ND (0.05) Outside ND (0.05) Array ND (0.05) ND (0.06) ND (0.06) ND (0.06) 96 ND (0.06) ND (0.06) T-A NS NS NS ND (0.06) ND (0.06) D Inside ND (0.05) D Array ND (0.05) 93 ND (0.05) ND (0.05) ND (0.06) ND (0.05) - ND (0.06) ND (0.05) T-A ft NS NS NS - Outside ND (0.06) Array ND (0.06) ND (0.05) D Diluted Sample ND () Not Detected (detection limit) NS Not Sampled Hazardous, Toxic, Radioactive Waste Page 19

21 PERFORMANCE DATA ASSESSMENT (1,2) The SPSH design verification study successfully achieved all of the criteria established for performance of the system. The performance criteria were: Heating the soil; Demonstrating removal of contaminants in the condenser effluent; and Demonstrated reduction of soil contamination. SPSH successfully heated soil in situ in all three arrays. Data collected from the thermocouples show that the soil was heated to near 100 C in each array. Once the soil was heated to the boiling point of water, the water within the soil turned to steam and was removed by the SVE system. Where soil moisture was not replaced, the conductivity of the soil decreased and the temperature of the soil decreased in the latter part of the test. Where there was adequate groundwater flow, the soil moisture and conductivity were maintained and the temperature remained near 100 C. SPSH removed significant quantities of contaminants as indicated by the condenser off-gas and condensate sample results. As shown in Table 8, the mass of solvents removed in the off-gas was significantly higher than the mass removed in the condensate. This difference is most likely due to the volatility of the contaminants present at this site. Table 8. Treatment Summary Soil Treated Contaminant Mass Removed Method 1 Contaminant Mass Removed Method 2 Array CY Tons in Off-Gas (lbs) 1 in Condensate (lbs) 2 Total (lbs) in Soil Pre-Treat in Soil Post-Treat Change (lbs) 3 1 1,260 2, ,230 2, ,420 2, Estimate based on total VOCs in off-gas. Mass was calculated daily using daily air flow rate through the condenser and contaminant concentration from the closest day that data was available. 2 Estimate based on total VOCs in the condenser water effluent. Mass was calculated daily using daily flow rate from the condenser and laboratory data from the closest day that data was available. 3 TCE, PCE, and TCA were used to calculate masses. Estimates are averages of soil concentrations found on site. Table 8 provides pre-and post-treatment contaminant masses for each array and the mass of contaminant observed in the SVE condenser off-gas and condensate (before treatment by catalytic oxidation and air stripping, respectively). Theoretically, the amount of contaminant reduction in the soil should equal the amount of contaminant removed by the SVE system. In reality, these amounts were not equal. Use of differing sampling and calculation methods most likely caused this difference. Condenser off-gas and condensate flow rates were available for every day the system was operating, but contaminant concentrations were available only every other day at best. For days where there were no sample results, results from the closest day that had results were used as the concentration for that day. Post-treatment soil samples were collected as near to the same location as the pre-treatment soil samples as possible. While this minimizes the introduction of variability, it cannot eliminate it. Considering the variability normally associated with environmental sampling, the results are considered representative. SPSH achieved significant reductions in soil contamination as measured by pre- and post- treatment soil sampling. Average contaminant removal rates are shown in Table 9 for soil inside and outside the arrays. Removal rates were greater than 90% for soil inside the first two arrays. Contaminant removals for PCE and TCE at array 3 were lower than arrays 1 and 2 possibly due to lower starting concentrations and increased soil resistivity. Use of a larger array increased soil resistivity and therefore resulted in less efficient soil heating. Hazardous, Toxic, Radioactive Waste Page 20

22 Table 9. Average Removal Efficiencies for Soil Remediation Ft. Richardson PRDA OU-B TCA PCE TCE Array Inside Outside Inside Outside Inside Outside 1 100% 96% 96% 96% 94% 92% 2 100% 99% 96% 84% 99% 85% 3 100% -198% 82% -332% 89% -49% Soil sample results from areas outside arrays 1 and 2 indicate that contaminant removal is significant but less efficient than inside the arrays. This may be due to the zone of heated soil not extending as far outside of the arrays as the radius of influence for the SVE system. The SPSH zone extended at least to the outside sampling point for arrays 1 and 2 (approximately 40% of the array radius, or 5 feet, beyond the array boundary); the SPSH zone did not extend as far (percentage wise) beyond the array boundary for array 3. The pre- and post-treatment soil sampling results indicated that the contaminant concentrations in several locations actually increased during the treatment period. Several negative removal rates were calculated. This is most likely a result of sampling variability and not an actual increase in the concentration of contaminants. Performance of the SPSH-SVE system was compared with performance of the SVE-only system, which was tested at OU-B in November This test involved extracting soil gas vapors from MW-14, located directly adjacent to array 1 (shown on Figure 2). Table 10 presents the range of total VOC concentrations in the condenser off-gas under test conditions with and without SPSH. The tests were conducted at similar vacuum flow rates. The concentration of total VOCs in extracted soil gas was significantly higher in samples collected during the SPSH study. This increase in VOC concentrations is attributed to the increased soil temperatures induced by the SPSH system. Table 10. Comparison of VOC Removal With and Without SPSH Test Total VOC Concentration (ppmv) SVE treatability study (without SPSH) Array 1 (SVE with SPSH) Array 2 (SVE with SPSH) Array 3 (SVE with SPSH) PERFORMANCE DATA QUALITY (4) The following QA/QC requirements were followed during the RI performed at OU-B: Applicable EPA sampling and analysis methods were used. Where EPA methods were not available, standard industry methods were used. Laboratory data packages included complete raw data deliverables and documentation sufficient to perform a USACE Level III data validation. QC samples and procedures were utilized by the off-site laboratory. A Level III data validation was performed on the off-site laboratory data. Guidelines recommended in EPA s Laboratory Data Validation Functional Guidelines for Evaluating Organic or Inorganic Analyses were followed. Hazardous, Toxic, Radioactive Waste Page 21

23 Duplicate samples were collected at a frequency of 10% and sent to the USACE Quality Assurance Laboratory for analysis. For generation of field screening data, applicable organic methods were used in the field laboratory and QC samples and procedures were utilized by the field lab. Rinsate blanks, field duplicates, and trip blanks were collected and submitted to the off-site laboratory for analysis to provide a means for assessing field QC. PROCUREMENT PROCESS (1,8) TREATMENT SYSTEM COST The SPSH study was implemented as a delivery order to a pre-placed indefinite delivery type architectengineer (IDT-AE) contract. As such, the scope of work for each array was defined by the government and negotiated with the contractor. The result of the negotiation was a firm-fixed price contract for accomplishment of the work described in the defined scope. Woodward-Clyde Federal Services was selected as the contractor to perform the SPSH study. Woodward- Clyde subcontracted with the following companies to perform the listed project tasks: Subcontractor/Equipment Vendor Current Environmental Solutions Tester Drilling Multichem Pye-Per Fuels Craig Taylor Rental NC Machinery H2Oil Tasks Treatment system vendor, monitoring the on-site computer Drilling operations Analytical laboratory Diesel fuel delivery Rental of 455 kw generator Rental of 1200 kw generator Rental of blower and air stripper TREATMENT SYSTEM COST (1,8) The total budgeted cost for this project was $967,822. Costs for each array includes installation of the electrode wells, thermocouple wells, and all ancillary equipment for operation of the system (generator, blowers, piping, etc.) All sampling, testing, and monitoring costs are also included. Table 11 summarizes the budgeted costs for the SPSH study. The contractor indicated that these costs were fairly close to the actual costs incurred. The contract price for the first array included costs for mobilization of the SPSH transformer equipment, a catalytic oxidizer for treatment of off-gas, and other startup and operational troubleshooting costs not included in subsequent arrays. Unit costs were calculated using the sum of the budgeted capital and operation and maintenance (O&M) costs. These unit costs are shown in Table 11. The soil treatment costs calculated for the treatability study at OU-B ranged from $189 to $288 per CY of soil treated or $103 to $158 per ton of soil treated. On a contaminant basis, the soil treatment costs ranged from $726 to $2,552 per pound of contaminant removed. Hazardous, Toxic, Radioactive Waste Page 22

24 Table 11. Cost Summary Cost Category Cost Element Array 1 Array 2 Array 3 Total Capital Costs ($) O&M Costs ($) Mobilization and Demobilization Planning and Preparation Subcontractors Site Work Startup and Testing O&M Labor Performance Testing and Analysis Equipment and Appurtenances Materials/Supplies 13, ,740 36,541 1,494 25, ,507 25,146 1,195 25,213 1,431 1, ,798 56, ,130 Fuel Capital + O&M Costs ($) (used to calculate unit costs) 363, , , ,284 Other Technology Specific Costs ($) Other Project Costs ($) Sampling IDW and DNAPL Travel Expenses Total Project Cost ($) 377, , , ,822 Treated Soil (CY) 1,260 1,230 1,420 3,910 Treated Soil (ton) 2,300 2,250 2,600 7,150 Contaminant Removed (lbs) Unit Cost ($/CY) Unit Cost ($/ton) Unit Cost ($/lb contaminant removed) ,056 1,123 2,400 2,552 1,088 1,277 5,362 8, ,090 8,532 3,961 Hazardous, Toxic, Radioactive Waste Page 23

25 For cost comparison purposes, the cost of treating the same soil (soil excavated from areas A-3 and A-4) in ex-situ static piles by heat enhanced SVE was $150 per CY not including excavation, sampling, and testing costs. The supplier of the technology reported that costs can be reduced to a range from $30 to $85 per CY of treated soil for easily accessible sites where commercial power is available. The cost of off-site disposal at the Defense Reutilization and Marketing Office is approximately $2,400 per CY, not including excavation or packaging. COST SENSITIVITIES (1) A significant portion of the operating cost of the treatment system came from the large power requirements of the treatment equipment. Because the site was in a remote location, power was provided by mobile, diesel fuel-powered electric generators. Because of this, fuel consumption and rental of the generators and storage tanks added a significant cost to the project that would not be incurred at sites where commercial electrical power is available. REGULATORY/INSTITUTIONAL ISSUES Because this project was performed under CERCLA regulations, it was not necessary to obtain permits from local regulatory authorities for on-site activities. It was necessary, however, to meet the substantive requirements of potentially applicable regulations. The following table lists the remedial action objectives for soil treated at OU-B. These objectives were established in the ROD. Chemical Table 12. Treated Soil Objectives (2) Performance Criteria (mg/kg) TCA 0.1 PCE 4.0 TCE None Provided The remedial objective for groundwater at OU-B is to reduce contamination to comply with Alaska s MCLs for drinking water. The applicable MCLs are provided in Table 4. TECHNOLOGY APPLICABILITY AND ALTERNATIVES APPLICABILITY OF THE TECHNOLOGY (2,3,7) The media of concern for evaluation in the FS at OU-B were the perched, shallow and intermediate groundwater intervals, and hot spot soil, all potential sources of continuing contamination to the deep aquifer at the site. The FS evaluation focused on contaminated soil and groundwater to a depth of 60 feet bgs. The depth of 60 feet bgs was chosen because it was deeper than the most highly contaminated groundwater, modeling showed that treatment to this depth would be sufficient to capture contaminants, and it is the depth below which specialized and overly expensive equipment would be necessary for trenching. Hazardous, Toxic, Radioactive Waste Page 24

26 A treatability study was performed that included pilot testing of SVE and air sparging. The SVE system was run for 5 days with the air sparging test conducted on the last day. Samples of extracted soil gas showed that SVE was effective at removing TCA and TCE, the designated indicator chemicals. With the air sparge blower on, TCE concentrations were increased in the SVE off-gas but TCA concentrations were not significantly affected. Although the SVE test was considered successful, the FS recommended that SVE treatment enhanced with in situ soil heating could be used at the site as a means for completing treatment more rapidly. USACE requested an analysis of heat enhancement methods. After a comparison of several different methods to heat the subsurface soil, electrical resistance (e.g., SPSH) was selected for evaluation at OU- B over radio frequency heating because it more efficiently delivers energy to the fine-grained soil found on site. This is important because, with either technology, electrical costs represent a significant portion of the total cost of remediation. SPSH simultaneously heats and ventilates soil in situ to remove volatile and semivolatile organic contaminants. SPSH is applicable for treatment of contaminated subsurface environments (soil, sludge, or sediments) in which contamination may be sorbed onto soil particles, dissolved in groundwater, or in the vapor phase. These media may be either fully or partially saturated with water. The process has been proven greater than 99% effective at removing VOCs in the vadose zone. COMPETING TECHNOLOGIES (2,7) The SPSH technology has many advantages over currently available and comparable technologies. There are several different accepted methods for heating subsurface soil. These include steam injection, use of radio frequency, and use of electrical resistance (e.g., SPSH). Steam injection is typically effective in more permeable and heterogeneous soil. High soil permeability is necessary to allow the steam to move through the soil. Steam injection was rejected as a potential heating technology at OU-B because contamination at OU-B is predominantly found in finer-grained soil. Radio frequency and electrical resistance heating methods work well with moist, fine-grained, lowpermeability soil. Soil heterogeneity is not necessary since steam is generated within the soil matrix. Both technologies require large amounts of electrical power, however electrical resistance heating is more efficient in delivering energy to the soil. Approximately 55% of the energy supplied by an electrical source is delivered to the soil by the radio frequency method compared to nearly 100% energy delivery by the electrical resistance method. In contrast to electrical resistance heating, radio frequency heating does not require the presence of water to carry electrical current. As a result, radio frequency heating can increase soil temperatures above 100ºC, the limiting temperature for electrical resistance heating. In addition, SPSH uses standard power frequency systems which are more robust and less expensive than higher frequency systems. At the time of this report, a treatability study was being conducted at Fort Wainwright, near Fairbanks, Alaska to compare the performance characteristics of radio frequency and SPSH. The SPSH process results in accelerated and more complete removal of target contaminants from soil when compared to conventional SVE treatment and does not require excavation. Compared to pump-and-treat systems, SPSH provides an increased rate and extent of remediation, reduced O&M costs due to shorter time on site, and is applicable to low-permeability, heterogeneous, and LNAPL/DNAPL-contaminated soil. In addition, SPSH has several advantages over excavation and ex-situ treatment. SPSH provides lower risk of contaminant exposure to humans and the environment, lower cost (20% to 30% of the cost of excavation and on-site treatment), and is applicable to sites with deep contamination (excavation is difficult below the water table). Hazardous, Toxic, Radioactive Waste Page 25